This application relates generally to processing of images and more particularly to processing images to identify points.
In various types of systems, images are formed and then processed. As a result of the processing, features of the image are detected.
For example, in electronic warfare (EW) systems infrared (IR) detectors are used to form images of objects. These systems are mounted on vehicles, such as aircraft. Processing of the IR image results in the detection of missiles heading towards the vehicle. The EW system can then take measures to jam the missiles so they do not strike the aircraft.
For the EW system to be effective, it must detect the missile while it is still relatively far from the aircraft. At this distance, the missile appears as a small point in the IR image. Thus, the EW system must be able to detect points in the image.
The problem of detecting points is made more difficult by large background variations in the image. Some methods of detecting points include first high pass filtering the image to remove background noise. However, conventional filters have a step response which may add spurious pulses to the residual image when certain image features are filtered.
According to another approach, the entire image is digitized without filtering. The pulses can then be detected using conventional correlation processing techniques. However, this approach requires an analog to digital converter with a very large dynamic range to resolve the small amplitude pulses from the very large amplitude background variations.
With the foregoing background in mind, it is an object of this invention to provide a filter which can detect pulses in an image.
It is further an object to provide a filter which does not introduce spurious signals into the filtered image.
It is yet another object to provide a filter useful in an EW system.
It is still further an object to provide a filter useful in any detecting system.
The foregoing and other objects are achieved by a multistage filter. The first stage produces a predefined output in response to an input pulse. The second stage produces a pulse output when the first stage produces the predefined output. The output of the second stage gates the portion of the input image containing the pulse to conventional circuitry for further processing.